In principle, it is a problem to operate semiconductor light-emitting elements, for example light-emitting diodes (LEDs) or LED systems, directly on an electrical power supply system, in particular when the semiconductor light-emitting elements are intended to be dimmable and to have at least approximately a sinusoidal current consumption.
Known approaches use step-up or step-down converters for adjusting a supply voltage for the semiconductor light-emitting elements. A filter capacitor is also used after the system rectification in order to keep the current in the semiconductor light-emitting elements at a virtually constant level. Such solutions are not dimmable. Furthermore, the current profile through the semiconductor light-emitting elements is not sinusoidal, which results in disadvantageous loading or undesirable interference on the AC system.
A further disadvantage consists in that a circuit without an energy store (filter capacitor) results in visible flicker in the connected light-emitting means. However, the filter capacitor also has the disadvantage that high charge-reversal currents reduce its life; therefore, the filter capacitor is often the weakest link in a circuit for actuating the light-emitting means.